Various types of defibering systems for paper and pulp processing are known. Typically, in these systems, cellulose fiber, in the form of dry pulp sheets or paper, is added to large volumes of water and continuously agitated during the defibering and pulping process. In these known systems, complete defibering of dry pulp sheets or clean recycle paper fiber sheets involves high process times, high energy consumption and large volumes of water.
Generally, in the present known defibering systems, the use of a wet process environment necessitates hydraulic processing where the process water contains 4 to 16% solid matter. In this wet environment, contaminants from the cellulose material mix with the process water and impede disassociation of the cellulose fibers. Furthermore, removal of the contaminants from the process water can create environmental hazards and effluent treatment problems.
In addition, the wet defibering and pulping processes are unable to recover many grades of paper for recycling because the paper may be resistant to the process water or cause other problems associated with the wet environment processing. As a result, many grades of paper that are difficult, expensive or incapable of being processed in a wet environment are disposed of in landfills or used in non-paper related end products, such as animal bedding.
For example, paper containing wet strength is manufactured to provide durability for long term weatherproof use in contact with moisture. As a result, wet strength paper is difficult to defiber and can cause block screens and pumps used in defibering the paper in wet pulp processing systems and are, typically, disposed of in landfills. Similarly, paper containing internal or surface latex is resistant to moisture and is virtually impossible to defiber using a wet environment. Currently, these latex paper products are not easily or economically recyclable using wet pulp processing systems.
In addition, biochemical oxygen demand (BOD) generating materials, such as starch, are added to most grades of paper to provide surface characteristics on the paper sheet to allow for clear printing and assist the bonding of the filler and cellulose. These materials are proportionally present in the effluent stream causing regulatory problems and creating a negative environmental impact on receiving stream quality. Since the presence of BOD generating materials in wet pulp processes creates significant environmental and effluent problems, government regulations have been introduced to reduce BOD content in waste streams. Therefore, due to these strict government regulations, the recycling of paper containing BOD generating materials in wet pulp processes may be reduced.
In present wet pulp processes, paper containing laser or toner type inks reduce brightness to the pulp or paper product and generally result in a high dirt count rendering the final product unacceptable. As the use of laser and toner type ink increases, recycling mills using wet pulp processing systems will be unable to maintain the quality of the final product. As a result, wet pulp processes designed to remove laser or toner inks will produce high volume waste streams that will increase cost and cause environmental hazards. In addition, paper containing high filler levels cause processing problems for some wet pulp processing systems. A high filler level can interfere with flotation, bleaching or screening of the wet fiber stock and, therefore, increase the erosion and abrasion on the process elements resulting in increased processing costs.
Therefore, there is a significant need for an improved method and device for addressing the operating problems that occur in wet pulping processes. This need intensifies as paper products that resist moisture are used, and as the government more stringently regulates the content of waste streams and effluent from paper processing mills.